The present invention relates to an ink jet head unit and a printer incorporating the same.
Japanese Patent Publication No. 3-224744A discloses an ink jet head unit (hereinafter, simply referred to as a head unit) provided with a damping chamber for absorbing ink pressure which is generated due to acceleration or the like while a carriage moves to carry the head unit.
The head unit is further provided with a filter disposed in an ink passage for preventing invaded foreign matter from flowing to the downstream side of the passage.
In such a head unit, air bubbles are accumulated in the damping chamber as a result of various causes. Such air bubbles tend to stay in a stagnant point in the ink passage, at which flow rate of the ink is zero or close to zero (e.g., in the vicinity of the filter where the area of the ink passage needs to be wider). In such a position, the air bubbles tend to grow larger.
In a case where the air bubbles which have grown under the high-temperature environment, for example, adhere onto the upstream side surface of the filter, the ink passage in the filter is clogged leading to a printing failure.
Further, an air bubble remaining in the damping chamber may be broken up into smaller bubbles due to vibrations or the like during the operation of the carriage. Such smaller bubbles may flow back into the ink passage of the upstream side of the head unit. In such a case, there is a possibility that the air bubbles may grow under the high temperature environment and enter the damping chamber again. As a result, the air bubbles may adhere onto the filter leading to the same problem as described above.
Japanese Patent Publication No. 9-300654A discloses a priming operation for discharging air bubbles with ink by forcibly sucking or compressing ink in the ink passage, thereby removing air bubbles in the ink passage. In order to enhance the reliability of the priming operation, the air bubbles to be discharged are passed through narrowed passages and broken up to smaller bubbles, thereby reducing discharging resistance. FIGS. 12 to 15 show such a structure.
As shown in FIG. 12, an ink supply case 200 is formed with an ink supply pipe 201 and an opening portion (ink supply port) 205 which connects the ink supply pipe 201 and an ink inlet 203 of a head chip 202. A nozzle section 204 in which a plurality of nozzle orifices are arrayed with a fixed pitch is provided on an end of the head chip 202 which is opposite to the end face 208 (FIG. 15) formed with the ink inlet 203.
As shown in FIGS. 13 and 15, a plurality of thin walls 211 are arrayed at the upstream side of the ink supply port 205. Each of the thin walls 211 extends perpendicularly to the extending direction of the ink supply port 205 (the ink inlet 203). The downstream side end of each thin wall 211 is placed so as to maintain a prescribed distance d from the end face of the head chip 202 having the ink inlet 203. Accordingly, a plurality of narrowed passages 212 each having a width e is formed at the upstream side of the boundary (end face 208) between the ink inlet 203 and the ink supply port 205.
As indicated by dashed lines in FIG. 14, the ink inlet 203 is an elongated rectangle having a width K and a height H2 which is considerably smaller than a height H1 of the ink supply port 205. Therefore, air bubbles tend to stay at the boundary 208.
In a case where air bubbles exist in the ink supply pipe 201, the air bubbles are moved toward the head chip 202 by the priming operation and broken up by the narrowed passages 212.
This publication, however, is silent about countermeasures for solving the above described problems (i.e., the case where the broken bubbles adhere onto the filter or flow back to the upstream side of the ink passage).
In addition, high machining accuracy and assembling accuracy are required for forming the narrowed passages 212 in the vicinity of the ink supply port 205 of the ink supply case 200 and for assembling the head chip 202 while maintaining the above-described distance d, resulting in a higher cost.